the branch of engineering science concerned with the design and construction of aircraft

Capable of happening, existing, or being true without contradicting proven facts, laws, or circumstances, Capable of occurring or being done in accordance with something specified. Used with the superlative, Permissible, noun_ A possible one, something that can be done, an applicant who might be suitable

thickly covered with ingrained dirt or soot

Free from danger or injury; undamaged or unhurt, Usable in specified conditions without being damaged. Often used in combination, (of an undertaking) secure from risk, noun_ contraceptive device consisting of a sheath of thin rubber or latex that is worn over the penis during intercourse, strongbox where valuables can be safely kept, A box, usually made of metal, in which valuables can be locked for safekeeping, transitive verb_ obsolete To render safe; to make right