first thing after waking up; upon rising
Refers to the time or action immediately after getting out of bed. Often used adverbially with に.
I make it a habit to drink a glass of water first thing after waking up.
Stretching right after getting up is good for the body.
Standard spelling using the common 起きる stem and がけ suffix.
Variant using the kanji 掛け for the suffix; less common but still seen.
Abbreviated kanji form; rare and may be confusing.
Compound of 起き (oki, stem of 起きる 'to get up') + がけ (gake, suffix meaning 'at the time of doing something'). The suffix がけ is related to 掛け (kake), indicating the start or onset of an action.