Webster's Revised Unabridged Dictionary · 1913

Sicker

Sicker , intransitive verb

[Anglo-Saxon sicerian.]

(Mining) To percolate, trickle, or ooze, as water through a crack. [Provincial English]

Sicker , adjective

[Old English siker; compare Old Saxon sikur, LG. seker, Dutch zeker, Danish sikker, Old High German sihhur, German sicher; all from Latin securus. See Secure, Sure.]

Sure; certain; trusty. [Obsolete or Provincial English & Scottish] — Burns
When he is siker of his good name. — Chaucer

Also: Siker

Sicker , adverb

Surely; certainly. [Obsolete]
Believe this as siker as your creed. — Chaucer
Sicker, Willye, thou warnest well. — Spenser

Also: Siker