6-Letter Words Starting: OP

• not transmitting or reflecting light or radiant energy; impenetrable to sight

• hard or impossible to understand

• in an open way

• challenge the accuracy, probity, or propriety of

• be against; express opposition to

• fight against or resist strongly

• contrast with equal weight or force

• set into opposition or rivalry

• act against or in opposition to

• be resistant to

• the branch of physics that studies the physical properties of light

• optical properties

• most favorable conditions or greatest degree or amount possible under given circumstances

• most desirable possible under a restriction expressed or implied

• an addictive narcotic extracted from seed capsules of the opium poppy

• used of mouth or eyes

• made open or clear

• not sealed or having been unsealed