Seed is partly gas-permeable (5)

I believe the answer is:

sperm

'seed' is the definition.
(thesaurus)

'partly gas-permeable' is the wordplay.
'partly' says the answer is hidden in the clue.
'SPERM' is hidden in the letters of 'gas permeable'.

'is' acts as a link.

(Other definitions for sperm that I've seen before include "Semen" , "Male reproductive cell" .)

I've seen this clue in The Independent.

Want a hint initially instead of a full solution? Install my app