Sleek

adj.capable, joyfulwarm

Meaning 1

Smooth, glossy, and shaped with clean flowing lines.

Reach for it when praising a polished visual or tactile finish

The sleek handrail curved continuously around the stair.

everyday
smooth
when an even surface is the factual quality
not when Smooth material can look plain and have none of sleek's polished line.
warm
glossy
when reflective shine is what catches the eye
not when Gloss alone can cover an awkward or bulky form.

Efficiently designed with little visible clutter or resistance.

Reach for it when describing a product or process whose refinement also serves function

The sleek booking tool exposes advanced choices only when they are needed.

playful
snazzy
when stylish novelty deserves informal praise
not when Snazzy favors conspicuous flair, nearly the opposite of restrained sleekness.
professional
minimalist
when deliberate visual reduction defines the style
not when Minimalism can remove useful features and still fail to be sleek.
professional
polished
when careful finishing and presentation are visible
not when Polish may conceal structural complexity rather than reduce it.
professional
streamlined
when shape or process reduces drag and clutter
not when Streamlined need not look luxurious or polished.
literary
elegant
when graceful simplicity joins beauty with fitness
not when Elegance is warmer and can flourish without a glossy surface.

sleek design
The sleek design keeps every maintenance point accessible.
sleek lines
Sleek lines make the small electric boat appear swift at rest.
sleek interface
A sleek interface is useful only if people can still find every action.

The definition and the example on this page are written here. The dictionaries above ground which meaning is being described, not the wording.