One very dead strand (7)
I believe the answer is:
isolate
'strand' is the definition.
(I've seen this before)
'one very dead' is the wordplay.
'one' becomes 'i' (Roman numeral).
'very' becomes 'so' (I've seen this in other clues).
'dead' becomes 'late' ('late' can be similar in meaning to 'dead').
'i'+'so'+'late'='ISOLATE'
(Other definitions for isolate that I've seen before include "Segregate or quarantine" , "Single out" , "Eat soil (anag)" , "Place or set apart" , "Detach" .)