Macrobius, Saturnalia 1.21:
They say that Adonis was killed by a boar, metaphorically representing the image of winter in this animal, because the bristly and rugged boar rejoices in wet, muddy spots covered in frost, and it properly feeds upon acorns, the produce of winter. Therefore, winter is something like the wound of the sun, which diminishes its light and heat for us: both of these things also happen to animals in death.
There is an image of this goddess fashioned on Mount Lebanon with a veiled head, a sad countenance, and holding her face behind her clothes with her left hand. It is believed that tears flow from her when people are looking. This image, in addition to being an image of a grieving goddess (as we have said), is also the image of the winter on earth when the land stands bereft of the sun, veiled by clouds, and the springs, those eyes of the earth, gush more abundantly while the fields, deprived of their cultivation, show their sad face. But when the sun comes from the lower parts of the earth and moves past the boundary of the spring equinox, lengthening the day, then Venus is happy and then spring forth fields green with crops, meadows with grass, trees with leaves. And it is for that reason that the ancients called April Venus.
Ab apro autem tradunt interemptum Adonin, hiemis imaginem in hoc animali fingentes, quod aper hispidus et asper gaudet locis humidis lutosis pruinaque contectis, proprieque hiemali fructu pascitur, glande: ergo hiems veluti vulnus est solis, quae et lucem eius nobis minuit et calorem: quod utrumque animantibus accidit morte. Simulachrum huius deae in monte Libano fingitur capite obnupto, specie tristi, faciem manu laeva intra amictum sustinens, lacrimae visione conspicientium manare creduntur: quae imago, praeter quod lugentis est, ut diximus, deae, terrae quoque hiemalis est, quo tempore obnupta nubibus sole viduata stupet, fontesque veluti terrae oculi uberius manant, agrique interim suo cultu vidui maestam faciem sui monstrant. 6 Sed cum sol emersit ab inferioribus partibus terrae, vernalisque aequinoctii transgreditur fines augendo diem: tunc est Venus laeta, et pulchra virent arva segetibus, prata herbis, arbores foliis. Ideo maiores nostri Aprilem mensem Veneri dicaverunt.