To climb in an awkward, effortful way, using both hands and feet. It suggests scrambling over something rather than moving smoothly.
Probably from an older form of "climb" with a -r ending, influenced by similar verbs like "slumber" and "flounder." The form emphasizes effort and awkwardness.
If "climb" is what a skilled hiker does, "clamber" is what you do when you’re out of shape and the rocks are loose. The extra syllable almost makes you feel the extra work in your muscles.
Complete word intelligence in one call. Free tier — 50 lookups/day.