Around 9 months or so, many infants understand that some words refer to specific objects. Although they can’t yet speak words, many infants will look at things or point at them when they hear certain words mentioned. For example, infants may look or point at a clock when they hear someone mention a clock (or a “tick-tock”). By 16 months, infants tend to look longer at objects or actions that have just been named for them.
Golinkoff, R., Hirsh-Pasek, K., Cualey, K., & Gordon, L. (1987). The eyes have it: Lexical and syntactic comprehension in a new paradigm. Journal of Child Language, 14, 23