There's supposed to be a spurt in language acquisition around 18 months, and Helen is doing that pretty much right on schedule. (Apart from her rapid and early acquisition of teeth, she seems to be timing pretty much everything "by the book", as well as sitting right on the median line on the growth charts.)
I've been trying to track the words she uses this month, but this will probably be the last time I do that now the rate of vocabulary acquisition has speeded up so much — it must be two or three words a day. This month has seen the first colours ("yellow") and numbers (she seems to understand "two") and shape words ("circle" and "square"), though she's still getting them sorted out properly. And Helen has started using possessives: in the morning she points at her bowl of cereal and says "Helen" and then at my bowl and says "mine", and the mug of tea we're going to take up to Camilla is "mummy". (I've started talking about myself in the third person - e.g. "Danny's" - to avoid the confusion of personal pronouns until she's ready to cope with that.)
The following list only includes words Helen has used: she clearly understands many more, but hasn't (for example) hit any contexts where she needs to use "sit" and "down" won't work just as well. The list also excludes words she's repeated once or twice but probably has no real understanding of, such as "gannet" and "puffin" and "vole". (This is of course an arbitrary judgement: she's not too precise on the duck-goose distinction and I'm pretty sure she doesn't understand that ducks form a non-monophyletic group and are not a clade.) I'm pretty sure I'm missing quite a few words even given those constraints - and I think she uses some words only at nursery, and probably other personal names as well.
bear, bee, bird, bug, bunny ("mama"), cat, cow, crab, dog, duck, fish, flower, frog, geese, grass, horse, leaf, lion, magpie, moon, octopus, owl, rain, ray, rock, shark, sheep, squirrel, starfish, tiger, tree, turtle, whale,
mummy/mama, dada, Helen, baby, mine (meaning "Danny's"), Rosie (the girl next door)
arm, chin, ear, eyes, foot, nose, hand, hair, teeth, toes,
boat, bus, bicycle, car, plane, truck, van,
bath, book, brush, ball, bubble, cloth, gate, door, hammer, home, house, net, pillow, slide, swing, sand, stick, sticker,
apple, banana, bean, blackberry, blueberry, bread, breadstick, chicken, egg, grape, milk, pear, water, yoghurt,
bib, bottle, bowl, chair, cup, fork, nappy, poo-poo, spoon, tray,
more, down, up, out, play, bang, splash, finish, put away, walk, back (meaning "put back together"),
bag, boot, button, dress, shoes, socks, hat, helmet, jacket,
yellow, two, square, circle,
Only the first syllable of many of the multi-syllable words is pronouncedUnstressed short syllables are mostly dropped, so "oct" for octopus and "but" for button, but banana is "nana" and yellow is "yellow". One consequence of that is that two or even more words can sound just the same - bread-stick, stick, and sticker are all pronounced "stick", most obviously, though some tests make it clear she knows the difference between them. And there's one special "baby talk" word, where she consistently uses "mama" to refer to rabbits, even though we use "bunny" or "rabbit".