IPA: /ˈklæm.bərər/
KK: /ˈklæm.bɚ.ɚ/
A person who climbs or moves in an awkward or laborious way, often using both hands and feet.
The clamberer struggled to reach the top of the steep hill.
Clamberer is formed from "clamber" (from Middle English "clamberen", meaning to climb awkwardly) and the suffix "-er" (meaning a person who). A clamberer is a person who climbs in an awkward or laborious manner.
Think of someone who is climbing awkwardly — that's what a clamberer does, as the root 'clamber' suggests an awkward climb.