English kill and ill (of Germanic but not IE root) seem to be strongly related to Basque (h)il(-du): either to die (intr.) or to kill (tr.). The h<->k transition seems quite common in proto-Basque, as well the h<->ø one.
English cub seems related to Basque kume (cub, whelp), in turn related to ume (child). An related word is probably Gaelic (Irish) cuib (originally cub, now nest), suggesting that the word arrived to modern British via the local (Celtizied) substrate.
Arguably Basque verbal suffix -tu (-du after consonant) could be related to English verbal preffix to (same sound).
Other possible connections:
- To carry: Basque ekarri (to bring, to carry away is eraman, i.e. "give-like": era-eman).
- To say: Basque esan (also erran in some dialects).
- suffix -er: a common Vasconic element in most West European languages.