From the Oxford English Dictionary:
Radical:
A adj. Of or relating to a root or to roots
1 a. Of, belonging to, or from a root or roots; fundamental to or inherent in the natural processes of life, vital
.....
b. Of a quality, attribute, or feature: inherent in the nature or essence of a person or thing; fundamental.
..... 
From "Die Zeit" of 29th January 2015:
The European reactions to the Greek elections show that what is growing together does not belong together. Tsipras' victory was celebrated by the French right radical Marine Le Pen and by the German party "Die Linke", by the Europe enemies Ukip and the left party Sinn Féin in Ireland, by the
right separatist Lega Nord from Italy and by the French ex-communist Jean-Luc Mélénchon, among others.
Obviously it arizes here in front of the European Establishment's eyes an "International of the Against", that not only trespasses without effort the borders between singular countries but also the one between right and left . The program of this right-left movement is the following: against Brussels, against The U.S.A., against Israel, against the N.A.T.O., against the so-called mainstream media, against any military intervention, against austerity, against globalization. And for: Putin.
The only manifest difference that complicates an association between the left radicals and the right radicals is Islam.
From the Open letter to German Citizens by Alexis Tsipras, published on the Handelsblatt, an economical newspaper, on 13th Januar 2015:
Greece's debt is currently unsustainable and will never be serviced, especially while Greece is being subjected to continuous fiscal waterboarding. The insistence in these dead-end policies, and in the denial of simple arithmetic, costs the German taxpayer dearly while, at once, condemning to a proud European nation to permanent indignity. What is even worse: In this manner, before long the Germans turn against the Greeks, the Greeks against the Germans and, unsurprisingly, the European Ideal suffers catastrophic losses.
....Our task is not to confront our partners. It is not to secure larger loans or, equivalently, the right to higher deficits. Our target is, rather, the country's stabilization, balanced budgets and, of course, the end of the grand squeeze of the weaker Greek taxpayers in the context of a loan agreement that is simply unenforceable. We are committed to end 'extend and pretend' logic not against German citizens but with a view to the mutual advantages for all Europeans.
Mrs. Katsulis phoning and speaking to politicians and journalists in a Greek political talk show on 14th January 2015:
Did you have to sleep without having dinner, Mr. Jatsidakis? Did you feel the banks thread of taking your hause away, that you built over the years? Did you sleep on a frozen mattress? What did you do to help all these people? I would like an answer. I have voted for Nea Demokratia for years and now I'm going to vote for Alexis Tsipras. Not because Alexis Tsipras would bring me to heaven. I trust on the purity of its words and its clean look. I don't trust that other ridiculous, evil and trickster. You lean your heads down, don't you? You have nothing to say, do you? I am a widow, I have a son that is studying and you give me a 360 Euros pension. And you want me to live on that. Give me an answer please! I am not the only one, we are a lot of Greek women that sleep in frozen houses and that have nothing to eat for dinner. Did I make my point clear, Mr. Jatsidakis? This is a cry of pain. If you want to know what the word of God says: "When pityful leaders command, then are people blessed. When the impure have the power, people suffer".