"Vishakha", like other Sanskrit terms, evokes a wide variety of English meanings - "forked", "two-branched", "poison vessel". Its alternative name is "Radha", which translates into "the delightful". Radha, as a name, has gained popularity by virtue of being the name of Krishna's beloved consort."
While Vishakha suggests "poison", rādhā means "the gift". This is interesting because it suggests a dual nature is going on now. As the energy moves up into the head area, in a saintly direction there is still a strong pull of body and mind identification that the ego has to deal with. Although Vishuddha (the throat chakra) means "purity", this is more in relation to how far the Kundalini has taken the seeker. We are now entering the Rudra granthis, the last knot of ego to be untied, and the toughest stage of all. The temptation of having all these powers to access the chakras through pranayama and other techniques becomes more and more of a threat to self-emancipation from the pull of Maya. Our higher Self is pulling us ever inward/up while our lower self (the pull of karma and the physical body with its survival instincts) pulling us outward/downward. It takes a lot of vigilance to stay the path at this stage (especially when spiritual experiences are not forthcoming to inspire us). The temptation here (and it increases as we go up to GV17 Mula) is to assert our ego more and more "I am in power" "I know everything" "This is mine!" - instead of "Thy will be done", "I am only an instrument in humble service"...
The throat chakra has the most petals on it compared to the other five below the crown and Sri Vasudeva has given workshops focused on this special chakra because it gives us the power to bring the forces of all the chakras through it, so we need to make a special effort here to speak with love, with noble intention, also with vitality. Here we have the combined gifts of Indra and Agni expressed as the power to achieve many and various fruits in life (vyapana shakti). At this stage the seeker has not yet given their "I" totally to the Divine and still has the freedom to choose evil or good actions, especially speech based on selfishness.
Speech is a particularly powerful carrier of a special kind of prana called shaktipat. It means the transmission of a more powerful energy to a weaker one. This is what true gurus give us in darshan or initiations, but we also do it to each other. A kind word can uplift and a harsh one can destroy - even moreso when the person has attained some measure of spiritual achievement.
This speaks to the root word of both Vishakha and Vishuddha: विशु Vizu/Vishu that means "in various directions," "in both directions," or "on both sides". We can go either way at this point. We can be full of ego (pingala, very active) or receptive and in humility (Radha, the perfect bhakti yogi).
Its main symbol as a decorative arch or gateway I think refers to this location as the beginning of the Rudra granthis point.
I think this is the essential idea of Vishakha.