“Sign” or “Sine” or “Syne”

sign s·AY·n

• nouna perceptible indication of something not immediately apparent (as a visible clue that something has happened).
• nouna public display of a message.
• noun(medicine) any objective evidence of the presence of a disorder or disease.
• nouna gesture that is part of a sign language.
• nouna fundamental linguistic unit linking a signifier to that which is signified; --de Saussure.
• nouna character indicating a relation between quantities.
• verbmark with one's signature; write one's name (on).
• verbapprove and express assent, responsibility, or obligation.
• verbbe engaged by a written agreement.
• verbengage by written agreement.
• verbcommunicate silently and non-verbally by signals or signs.
• verbplace signs, as along a road.
• verbcommunicate in sign language.

sine s·AY·n

• nounratio of the length of the side opposite the given angle to the length of the hypotenuse of a right-angled triangle.

syne

No dictionary entry for this spelling — see the usage examples below for how it shows up in writing.