Used attributively before a noun to describe something characteristic of summer.
Definitions
Characteristic of or suitable for the summer season. Light fabrics like cotton are perfect for summertime wear.
Used informally to mean 'during the summer'.
Definitions
During the summer season; in the summertime. They rent out their cottage wintertime and stay there themselves summertime.
Synonyms
in summer
in the summer
during the summer
during summer
throughout the summer
in the summertime
over the summer
during the summer months