inner interner interior

in⋅ner

    [in-er] 

–adjective

1.	situated within or farther within; interior: an inner door.

2.	more intimate, private, or secret: the inner workings of the organization.

3.	of or pertaining to the mind or spirit; mental; spiritual: the inner life.

4.	not obvious; hidden or obscure: an inner meaning.

Origin: 
bef. 900; ME; OE innera, comp. based on the adv. inne within, inside; see inmost, -er ⁴ 

Related forms:

in⋅ner⋅ly, adverb, adjective

in⋅ner⋅ness, noun

                   

in⋅ter⋅nal

    [in-tur-nl] 

–adjective

1.	situated or existing in the interior of something; interior.

2.	of, pertaining to, or noting the inside or inner part.

3.	Pharmacology. oral (def. 4).

4.	existing, occurring, or found within the limits or scope of something; intrinsic: a theory having internal logic.

5.	of or pertaining to the domestic affairs of a country: the internal politics of a nation.

6.	existing solely within the individual mind: internal malaise.

7.	coming from, produced, or motivated by the psyche or inner recesses of the mind; subjective: an internal response.

8.	Anatomy, Zoology. inner; not superficial; away from the surface or next to the axis of the body or of a part: the internal carotid artery.

9.	present or occurring within an organism or one of its parts: an internal organ.

–noun

10.	Usually, internals. entrails; innards.

11.	an inner or intrinsic attribute.

Origin:  1500–10; < class="ital-inline" style=" color: rgb(77, 78, 81); line-height: 1.25em; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; display: inline; font-style: italic; font-family:verdana;font-size:100%;">internālis, equiv. to L intern(us) intern ³ + ālis -al ¹

Related forms:

in⋅ter⋅nal⋅i⋅ty, in⋅ter⋅nal⋅ness, noun

in⋅ter⋅nal⋅ly, adverb

in⋅te⋅ri⋅or

    [in-teer-ee-er] 

–adjective

1.	being within; inside of anything; internal; inner; further toward a center: the interior rooms of a house.

2.	of or pertaining to that which is within; inside: an interior view.

3.	situated well inland from the coast or border: the interior towns of a country.

4.	of or pertaining to the inland.

5.	domestic: interior trade.

6.	private or hidden; inner: interior negotiations of the council.

7.	pertaining to the mind or soul; mental or spiritual: the interior life.

–noun

8.	the internal or inner part; inside.

9.	Architecture. a. the inside part of a building, considered as a whole from the point of view of artistic design or general effect, convenience, etc. b. a single room or apartment so considered.

10.	a pictorial representation of the inside of a room.

11.	the inland parts of a region, country, etc.: the Alaskan interior.

12.	the domestic affairs of a country as distinguished from its foreign affairs: the Department of the Interior.

13.	the inner or inward nature or character of anything.

14.	Mathematics. the largest open set contained in a given set, as the points in a circle not including the boundary.

Origin:  1480–90; < class="ital-inline" style=" color: rgb(77, 78, 81); line-height: 1.25em; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; display: inline; font-style: italic; font-family:verdana;font-size:100%;">inter- inward + -ior comp. suffix;see exterior 

Related forms:

in⋅te⋅ri⋅or⋅i⋅ty   [in-teer-ee-awr-i-tee, -or-]  noun

in⋅te⋅ri⋅or⋅ly, adverb

Synonyms: 8. See inside. 

Antonyms: 1, 8. exterior.

here is Examples showing some difference of the meaaning and usage of  "Inner" and "Internal":

"Inner Diameter" of a pipe also can be said "Internal Diameter". It means the Diameter of the Inside Round or inside track.

 

While "Internal Coating" of a pipe, here, means the coating within the surface. like "4.

existing, occurring, or found within the limits or scope of something; " or "- happening or arising or located within some limits or especially surface " "Inner coating" can't replace the "internal coating" here, or it would be rather the meaning that "the coating for inside wall" of a pipe. Another example is about the usage: "Inner Land" indicats the meaning of "remote", and in the above  dictionary it is said "within or farther within" "Internal land" is ambiguous about the indication of remote location.