Monotonous comes from Greek "monotonos". Greek "monotonos" is a compound made from the word "monos" which means single and "tonos", pitch, key, or musical scale in which a piece of music is composed.

The old English spelling of the word was "ūtlendisc". The sound (sh) was spelled "sc" in old English times. In Old English "ūtland", literally "out-land", meant "foreign country".

Vigilant comes from the Latin word "vigiāns", the present participle of the Latin verb "vigilāre", which means "to be watchful".

The English word meticulous originally meant "fearful". Because a person who is fearful of making a mistake will take great care while performing a task, meticulous came to mean "extremely careful". It comes from the Latin word "metīculōsus, "fearful".

Furtive comes from the Latin word "furtīvus", which can mean both "obtained by theft" and "stealthy"."Furtīvus" is related to the Latin words "furtum", theft and "fur", thief.

Conspicuous comes from the Latin adjective "cōnspicuus". "Cōnspicuus" itself comes from the Latin verb "cōspicere", to notice, catch sight of". Cōn- meaning "completely, throughly" and the verb specere, meaning "to see".

Conspicuous means, easily seen; obvious. Attracting attentions; striking; remarkable.

Egregious comes from Latin "ēgregious", standing out. Latin "ēgregious" itself is made up of the Latin prefix ē- (the form that the prefix ex-, "out", takes before consonants), and greg-, a form of the Latin word grex, "herd".

Apprehensive comes from the Latin verb, "apprehendere", to seize. "Apprehendere" is also the source of English apprehend.