Synonyms of the word

undependable

• adj. Not dependable.

erratic

• adj. unsteady, random; prone to unexpected changes; not consistent.
• adj. Deviating from the common course in opinion or conduct; eccentric; odd.
• n. (geology) A rock moved from one location to another, usually by a glacier.
• n. Anything that has erratic characteristics.

fallible

• adj. Capable of making mistakes or being wrong.

temperamental

• adj. (not comparable) Of, related to, or caused by temperament.
• adj. Subject to changing and unpredictable emotional states; moody, capricious; sometimes used figuratively…

uncertain

• adj. Not certain; unsure.
• adj. Not known for certain; questionable.
• adj. Not yet determined; undecided.
• adj. Variable and subject to change.
• adj. Fitful or unsteady.
• adj. Unpredictable or capricious.
• n. (with "the") Something uncertain.

unreliable

• adj. Not reliable.

unsound

• adj. Not sound, particularly.

untrustworthy

• adj. Not deserving of trust; unreliable.

untrusty

• adj. Not trusty.