Frank and candidly straightforward / Generous and kind / Emotionally receptive

A person who opens something. / A device that opens something; specifically a tin-opener/can-opener, or a bottle opener. / (in combination) An establishment that opens.

completely open / having no laws or law enforcement / unsettled or unresolved / vulnerable or unprotected / (sports) without the presence of opponents nearby

In an open manner, visibly, not covertly.

(grammar) A compound word with spaces in it, for example, high school, school bus, or science fiction.

(mathematics, physics) A differential operator,denoted ∆ and defined on ℝⁿ as 𝛥=∑ᵢ₌₁ⁿ(∂²)/(∂x_i²), used in the modeling of wave propagation, heat flow and many other applications.

A house habitually kept open to callers. / An event, often in one's home, at which there are few restrictions regarding who and how many may attend.

(sometimes attributive) Creative work that others can freely and legally copy or modify.

(colloquial) A person or thing's normal mode of operation.

Of or relating to operations, especially military operations. / Functioning and ready for use. / Effective or operative. / Determined by means of practical measures.