Starts to offer various union members a cell (4)

I believe the answer is:

ovum

'a cell' is the definition.
(an ovum is an egg cell)

'starts to offer various union members' is the wordplay.
'starts to' suggests taking the first letters.
The first letters of 'offer various union members' is 'OVUM'.

(Other definitions for ovum that I've seen before include "Female gamete" , "bit of life potentially" , "A female egg-cell" , "Human egg cell" , "Female reproductive cell" .)

I've seen this clue in The Daily Express.

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