What's the difference between sumless and sunless?

Sumless

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Definition:

• (a.) Not to be summed up or computed; so great that the amount can not be ascertained; incalculable; inestimable.

Example Sentences:

Sunless

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Definition:

• (a.) Destitute or deprived of the sun or its rays; shaded; shadowed.

Example Sentences:

• (1) Dihydroxyacetone-containing sunless or self-tanning topical preparations are enjoying a resurgence of use in recent years.
• (2) The surgical masks being distributed across the nation will do almost nothing to protect those living in a sunless smog.