Let net tangle, to irritate (6)
I believe the answer is:
nettle
'to irritate' is the definition.
(synonyms)
'let net tangle' is the wordplay.
'tangle' is an anagram indicator.
'let'+'net'='letnet'
'letnet' anagrammed gives 'NETTLE'.
(Other definitions for nettle that I've seen before include "Annoy - stinger" , "Stinging plant; annoy" , "To be annoying" , "Clasp it firmly and it will not sting" , "sample of herbal tea?" .)