ACK bf70224 (Haven't checked for proper replacement in all places but I imagine check-doc would catch that.)

src/rpc/blockchain.cpp: " "cost" : n (numeric) The block cost\n"
src/rpc/mining.cpp: " "currentblockcost": nnn, (numeric) The last block cost\n"
src/main.cpp: return state.DoS(100, error("ContextualCheckBlock(): cost limit failed"), REJECT_INVALID, "bad-blk-cost");

etc.

Hmm, what about using the term "blockcost" instead?

@paveljanik yes if you want to change all occurrences, also in variable names, then there is much more code impact.

Bah, changing all occurences of 'cost' to 'weight' is a huge change.
I'm also having second thoughts about it.
Changing it just in user-facing messages is doable, but yes it also appears in the RPC API, in variable names, in tons of comments. And I suppose those all have to be changed for consistency.