Step 1: Set up what we know.
The first word is "illicit" (7 letters: i-l-l-i-c-i-t). The fourth word must be "licit" (5 letters: l-i-c-i-t). Since the fourth word comes right after the third word, and each step is exactly one add, delete, or replace move, the third word must turn into "licit" using exactly ONE such move. So the real test for each option is simple: can this candidate word become "licit" using only one delete, add, or replace?
Step 2: Test "Implicit".
"Implicit" has 8 letters (i-m-p-l-i-c-i-t). To reach "licit" (5 letters), we would have to remove three letters at once, "i", "m", and "p", from the front. One operation removes only one letter, so this cannot be done in a single move. "Implicit" is ruled out.
Step 3: Test "Explicit".
"Explicit" has 8 letters (e-x-p-l-i-c-i-t). Turning it into "licit" needs the removal of three letters, "e", "x", and "p", from the front, again three deletions bundled into one step. A single operation cannot do this. "Explicit" is ruled out.
Step 4: Test "Enlist".
"Enlist" has 6 letters (e-n-l-i-s-t). To become "licit" (l-i-c-i-t), we would need to drop "e" and "n" from the front (two deletions) and also swap the "s" for a "c" (a replacement). That is well more than one operation, so "Enlist" cannot become "licit" in a single step either.
Step 5: Test "Elicit".
"Elicit" has 6 letters (e-l-i-c-i-t). Comparing it letter by letter with "licit" (5 letters, l-i-c-i-t), simply deleting the very first letter "e" from "Elicit" gives exactly "licit". That is a single delete operation, nothing more. "Elicit" works.
Step 6: Note the fifth option for completeness.
"Inlist" (6 letters: i-n-l-i-s-t) has the same problem as "Enlist": two extra letters up front ("i", "n") plus an "s" that must become "c", which is again more than one move. It cannot be the answer either.
Final Answer:
Only "Elicit" can become "licit" using exactly one operation, so it is the word that fits as the third word in the sentence.
\[ \boxed{\text{Elicit}} \]