Synonyms of the word

unflagging

• adj. Never tiring or lacking energy; without rest; without slowing.

constant

• adj. Unchanged through time or space; permanent.
• adj. Consistently recurring over time; persistent.
• adj. Steady in purpose, action, feeling, etc.
• adj. Firm; solid; not fluid.
• adj. (obsolete) Consistent; logical.
• n. That which is permanent or invariable.
• n. (algebra) A quantity that remains at a fixed value throughout a given discussion.
• n. (sciences) Any property of an experiment, determined numerically, that does not change under given circumstances.
• n. (computing) An identifier that is bound to an invariant value; a fixed value given a name to aid in readability…

energetic

• adj. Possessing, exerting, or displaying energy.
• adj. Of or relating to energy.

indefatigable

• adj. Extremely persistent and untiring.

tireless

• adj. Indefatigable, untiring and not yielding to fatigue.
• adj. Without a tire (wheel covering); tyreless.

unfailing

• adj. inexhaustible.
• adj. changeless.
• adj. infallible.

unwearying

• adj. Untiring; not becoming tired.