The most common and most likely answer to this crossword clue is the 5 letter word FEINT
I've seen this crossword clue in The Daily Telegraph
F
E
I
N
T
Buddy explains!

The straight part
We know that "pretence" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pretence = feint.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FEINT mean?
FEINT noun- A movement made to confuse the opponent; a dummy.
- That which is feigned; an assumed or false appearance; a pretense or stratagem.
- (war) An offensive movement resembling an attack in all but its continuance
- To make a feint, or mock attack.
- Feigned; counterfeit.
- (war) (of an attack) directed toward a different part from the intended strike
- The narrowest rule used in the production of lined writing paper.