Crossword Genius

Undertaking to put pressure on sill (6)

Ross

I believe the answer is:

pledge

'undertaking' is the definition.
(I've seen this before)

'pressure on sill' is the wordplay.
'pressure' becomes 'p' (abbreviation).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'sill' becomes 'ledge' (I've seen this in another clue).
'p'+'ledge'='PLEDGE'

'to put' acts as a link.

(Other definitions for pledge that I've seen before include "Vow, affirm" , "Promise, word of honour" , "Solemn undertaking" , "Covenant" , "Promise solemnly and formally" .)

I've seen this clue in The Mirror.
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