Print something penetrating! (7)
I believe the answer is:
stencil
'print' is the definition.
(stenciling is a kind of printing)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for stencil that I've seen before include "Cut-out for painting patterns or shapes" , "means of decoration" , "Sheet with cut-out letters, pattern etc for copying" , "Text template" , "Reproduction device for clients" .)