The most common and most likely answer to this crossword clue is the 4 letter word POSE
P
O
S
E
More clues leading to the result POSE
- Model of Greek sea god only half complete
- Present writer adopts son
- Heard about US writer’s affectation
- Suggest being part of strike, so people rise up
- American writer capturing southern attitude
- Model to disapprove of, not given work
- Model, outsize, getting into exercise
- Storyteller turned up without a present
- Author Edgar maintains society attitude
- Starts to put on sexy exhibition?
Buddy explains!

The straight part
We know that "act" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case act = pose.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 POSE mean?
POSE noun- Common cold, head cold; catarrh.
- Position, posture, arrangement (especially of the human body).
- Affectation.
- To place in an attitude or fixed position, for the sake of effect.
- To ask; to set (a test, quiz, riddle, etc.).
- To constitute (a danger, a threat, a risk, etc.).
- (in the phrase "to pose as") To falsely impersonate (another person or occupation) primarily for the purpose of accomplishing something or reaching a goal.
- To assume or maintain a pose; to strike an attitude.
- To behave affectedly in order to attract interest or admiration.
- To interrogate; to question.
- To question with a view to puzzling; to embarrass by questioning or scrutiny; to bring to a stand.
- To ask (someone) questions; to interrogate.
- To puzzle, non-plus, or embarrass with difficult questions.
- To perplex or confuse (someone).