This is the 700th most frequent Czech word.
syna
"Syna" means "son" in English, in the accusative or genitive case in Czech.
In this sentence, "syna" is used in its accusative case to indicate that the son is the direct object of the verb "vidím" (I see).
Vidím svého syna na hřišti.
I see my son on the playground.
Here, "syna" is used in its genitive/dative case to indicate possession or to whom the action of 'asking' pertains.
Ptala jsem se syna na jeho školní den.
I asked my son about his school day.
"Syna" here takes the accusative form following the verb "hledat" (to look for), marking it as the object of the search.