This is the 1041st most frequent Russian word.
мосту
"Мосту" means "to the bridge" (dative case of "мост").
The word "мосту" is in the dative case used to indicate a direction towards the bridge.
Мы подойдём к старому мосту завтра.
We will approach the old bridge tomorrow.
Here, "мосту" is in the dative case indicating movement or usage of the bridge as a path.
По мосту мы прошли на другую сторону речки.
We walked across the bridge to the other side of the river.
In this sentence, "мосту" is in the dative case as part of a construction with the verb "приступить," which governs this case.