Climber I swear needs it when slipping (8)
I believe the answer is:
wisteria
'climber' is the definition.
(the wisteria is a climbing plant)
'i swear needs it when slipping' is the wordplay.
'needs' is a charade indicator (letters next to each other).
'when slipping' indicates anagramming the letters.
'i'+'swear'+'it'='iswearit'
'iswearit' anagrammed gives 'WISTERIA'.
(Other definitions for wisteria that I've seen before include "Climber" , "Climbing lilac-flowered shrub" , "climbing plant" , "Large climbing shrub, often attached to house" , "Vine with pendulous clusters of flowers" .)