I am afraid I can't recommend any "fun" and "gamey" type activities. We went the old-fashioned way.
Read together (one page DD, one page me) stuff that was more advanced vocabulary wise than what she'd read on her own (or even if she'd read it, she wouldn't check out meaning of words she didn't know, would just use context), underlined words she wouldn't know or what I would say "interesting" words, made flash cards for those with including definition, synonym/antonym and then kept a box of these and kept coming back to them. We did max 5 words per reading (otherwise it becomes a chore) and would aim to learn 10-15 new words per week + reviewing words from previous weeks. You can buy a plastic box (index card box?) + dividers at WH Smith and keep it on the dining table. We had three sections - new, kind of know the meaning but not getting them 100% consistently, and still learning. Then we'd shuffle cards from section to section depending on progress.
It also makes sense to learn Latin and Greek prefixes, suffixes and roots for the main ones like bio, geo, graph, psyche, etc - makes it easier to guess/derive meaning that you don't know.
The reading together also helped with comprehension/writing as we'd also discuss literary techniques, kept a note of amazing metaphors/similes etc.
Key is to keep this balanced and turn bedtime reading into a chore but you don't actually have to do this for hours - as long as it's regular, mid of Yr5 should give one plenty of time.
Another thing is you have to read non-fiction as well as there is specific vocab that you won't find in fiction - we read Aquila, How it Works, Discovery Box, cooking books (when cooking, great for weird ingredients), First News and also some adult newspapers/magazines (very limited) as the latter would often have really advance vocab (e.g. a smallish article from the Economist, The Week, etc)